Various types of memory have conventionally been proposed. As typical memory, the following can be given: memory including an electromagnetic tape or an electromagnetic disk, RAM capable of writing and reading, ROM only for reading (read only memory), and the like.
As conventional ROM, the following can be given: mask ROM which stores information with a mask in an IC manufacturing process, fuse-type ROM which stores information by melting down a fuse element with current after manufacture of an IC chip, antifuse-type ROM which stores information by short-circuiting an insulator with current after manufacture of an IC chip, and the like.
Since mask ROM stores information with a mask in an IC manufacturing process, a mask corresponding to information to be written has to be prepared, and thus, manufacturing cost has been increased. In addition, fuse-type ROM could cause malfunction due to dust generated when a fuse element is melted down.
In addition, antifuse-type ROM is more advantageous than other ROM because the antifuse-type ROM does not need a mask corresponding to information to be written at manufacture and dust is not generated when information is written to the memory. Note that the fuse-type ROM and the antifuse-type ROM differ from the mask ROM in that data can be added. In addition, the fuse-type ROM and the antifuse-type ROM can also be referred to as write-once-read-many memory. As an example of antifuse-type ROM formed over a silicon substrate, a technique described in Patent Document 1(: Japanese Published Patent Application No. H7-297293) is given.
FIG. 15 shows a cross-sectional view of antifuse-type ROM disclosed in Patent Document 1. In FIG. 15, a silicon substrate 50 over which an nMOS transistor is formed, an amorphous silicon film 53, a tungsten film 54, a tungsten film 54′, and an Al—Si—Cu wiring 55 are formed. Although reference numerals 51 and 52 are not clearly identified in Patent Document 1, the reference numeral 51 is probably an n+ drain region and the reference numeral 52 is probably a SiO2 film formed by a CVD method. Patent Document 1 is characterized in that the tungsten film 54′, the amorphous silicon film 53, and the tungsten film 54 which form a stacked film are consecutively formed with a multi-chamber system without being exposed to the air.
In recent years, a semiconductor device with a wireless communication function, specifically a wireless chip, has been expected to have a large market, thereby having attracted attention. Such a wireless chip is referred to as an ID tag, an IC tag, an IC chip, an RF (radio frequency) tag, a wireless tag, an electronic tag, and an RFID (radio frequency identification) in accordance with usage.
A wireless chip includes an interface, memory, a control portion, and the like. As the memory, RAM capable of writing and reading and ROM only for reading are used, and they are separately used in accordance with purposes. Specifically, a memory region is assigned for each specified application, and an access right is managed for each application and each directory. In order to manage the access right, the wireless chip has a verification unit which compares and verifies a private code of application and a control unit which gives users the access right regarding the application to which the private code is identical, according to the comparison and verification by the verification unit. Such a wireless chip is formed using a silicon wafer, and integrated circuits such as a memory circuit and an arithmetic circuit are integrated over a semiconductor substrate.
When a card to which such a wireless chip is mounted (a so-called IC card) is compared to a magnetic card, the IC card has advantages of having a large memory capacity, an arithmetic function, high authentication accuracy, and great difficulty in falsification. Therefore, the IC card is suitable for management of personal information. ROM only for reading is commonly used as memory mounted to an IC card so that falsification is impossible.